Spark plug with conical seat sealing washer



Jan. 11, 1966 M. E. POLAND SPARK PLUG WITH CONICAL SEAT SEALING WASHER File'd Aug. 29, 1962 INVENTOR. MILTON E. POLAND ATTORNEYS United States Patent i 3,229,144 SPARK PLUG WITH CONICAL SEAT SEALING WAdl-IER Milton E. Poland, Royal Oak, Miclr, .assignor to Champion Spark Plug Company, Toledo, Ohio, a corporation of Delaware Filed Aug. 29, 1962,8211. No. 220,229 7 Claims. (Cl. 3,1-3138) The present invention relates to electrical discharge devices; and more particularly to igniters capable of withstanding t he extreme temperature and thermal shock conditions which are experienced in rockets and jet engines.

A device of the type involved generally comprises a metallic tubular casing member having a metallic electrode positioned in its central opening, and one or more ceramic sleeves to insulate the electrode electrically from the casing member. 'Heretofore a molten glass has been used in such devices for effecting a seal between. the ceramic insulating sleeves, and the electrode and casing members; so that all of the prior art devices have use limitations as determined by the glass type seals.

An object of the present invention is the provision of a new and improved spark plug or igniter suitable for general use, and capable of withstanding even the extreme thermal shock conditions involved in rocket engines and the like, and in which the ceramic parts are bonded to the metal parts by means of a metallic braze.

A difficult problem exists in the bonding of a metal to a ceramic body by means of a molten braze, inasmuch as all of the commercially used brazing metals have coefficients of expansion which are considerably greater than commercially used ceramic insulator bodies.

A further object of the present invention is the provision of a new and improved igniter device of the above described type wherein its metallic seals are so constructed and arranged as to produce an absolute of force upon the ceramic insulator body as a consequence of temperature changes.

A still further object of the present invention is the provision of a new and improved construction of an igniter of the above-described type, and which is so constructed that an appreciable thickness of brazing material can be placed in the regions where seals are desired, and the entire assembly exposed to a sufiicient temperature 0 melt the brazeduring which melting operation the parts move relative to each other in a manner which automatically centers the parts and provides a uniform metallic bond of minimum thickness between the various elements.

Further objects and advantages of the present invention will become apparent to those skilled in the art to which it relates from the following description of the preferred embodiment described with reference to the accompanying drawing forming a part of this specification, and in which:

FIG. 1 is a longitudinal cross sectional view of an igniterthe view including fragmentary portions of a surrounding supporting structure;

FIG. 2 is an isometric view of a metal washer used to effect part of the seal shown in FIG. 1;

FIG. 3 is a fragmentary cross sectional view of another embodiment of the invention which utilizes another form of sealing arrangement; and

FIG. 4 is a cross sectional view of an annular metal washer that is used as part of the sealing structure shown in FIG. 3.

While the invention may be otherwise embodied, it is herein shown and described as embodied in an igniter capable of use in the extreme temperature and thermal shock conditions found in present day rocket engines.

According to principles of the present invention, it has been discovered that the ceramic insulator of an igniter 3,229,144 Patented Jan. 1.1, 1966 can be sealed to the metal parts which it separates by means of commercially available brazing materials, provided an absolute minimum thickness of brazed joint .is utilized, and provided the brazed joints are so arranged as to avoid being placed under any appreciable amount of tension. Inasmuch as brazing operations are usually carried out by placing the parts to be brazed in a furnace where the parts cannot be manually manipulated, it is a further feature of the invention that the parts are so constructed that they automatically center themselves during the melting of the brazing metal to produce an absolute minimum thickness of sealing metal.

The igniter shown in FIG. 1 generally comprises a metal tubular sleeve or casing A that is enlarged adjacent its outer end to provide a tapered shoulder 10 by means of which it is positioned within a receiving opening 12 in a housingstructure 14. The inner end of the housing structure 14 extends through an opening 16 in the sidewall of a rocket casing 18 and is afiixed thereto in a manner well known to those skilled in the art. A central opening 20 extends through the casing A and is enlarged in an outer end portion 22 to provide a shoulder 24 which is preferably conically shaped. A small diameter inner end portion 26 of the opening 20 is accurately' machined into a smooth cylindrical surface for reasons which will later be described.

The igniter shown in the drawing further includes a generally tubular ceramic insulator body B that is positioned within the central opening 20 of the casing member A. The insulator body B is also enlarged adjacent its outer end 28 to provide a conical shoulder 30 that is accurately shaped to match the shoulder 24 of the casing A. The small diameter section of the insulator body B has a diameter which is appreciably less than the inner end of the opening .20 of the casing A so as to provide an appreciable clearance 32 therebetween-except in the area adjacent the lower inner end of the insulator body where an annular projection 34 is provided for the purpose of centering and guiding the lower end of the insulator body relative to the casing member A. The insulator body B is also provided with a central or axially extending, opening 36 therethrough. The opening 36 is also enlarged adjacent its outer end, as at 38, to also provide a conically shaped outwardly facing shoulder 40 for reasons which will later be explained.

The igniter structure. is generally completed by means of a metallic center electrode structure C which extends generally through the central opening 36 0f the insulator body B for the purpose of conducting a high voltage current to the inner end of the igniter assembly. The electrode structure C generally comprises a cylindrical rod 42 that is provided with an integral collar 44 that is seated against the bottom end surface 46 of an intermediate, radially enlarged. section 48 of the central opening 36. The portion of the rod 42 that includes the collar 44, and which extends upwardly therefrom, is made from what is known in the art as a Kovar type metal which has a coefiicient of expansion generally matching that of ceramic bodies, and more particularly alumina insulator bodies. Kovar metals are iron-base alloys comprising approximately 29% nickel, 17% cobalt, 0.3% manganese, and perhaps other minor constituents, and have an average co-efficient of thermal expansion, between F. and 1000 F., of approximately 3.70 10 inches per inch per degree Fahrenheit. A portion 52 of the rod 42,, below the collar 44, is made of a dissimilar metal which may be a stainless steel in order to be resistant to the erosive forces of the electrical are that is produced adjacent its lower end. The portions 50 and 52 of the electrode 42. are suitably attached, as by means of a resistance weld.

The electrode structure C is completed by means of a washer or eyelet 54 that is positioned around the rod 42' in general abutment with the conical shoulder 40 of the insulator B. The eyelet 54 is metallically bonded to the portion 50 of the rod 42 by means of a brazed joint 56. The outer conical surface 58 of the washer 54 is metallically bonded to the conical shoulder 40 of the insulator body B by means of a brazing operation which will later be explained. In the embodiment shown in the drawing, the metal casing A is made from a type 446 stainless steel having an average coefficient of thermal expansion between the temperatures of 80 F. and 1000 F. of 5.8 inches per inch per degree Fahrenheit; and the ceramic insulator body B is made from a high alumina ceramic material having a co-efficient of expansion between 80 F. and 1000 F. of 3.88 10- inches per inch per degree Fahrenheit.

The surfaces of the shoulders 30 and 40 of the insulator body B are metallically bonded to the shoulder 24 and the conical surface 58, of the casing A and washer 54, respectively, by means of What is essentially a brazing operation. The shoulders 30 and 40 of the ceramic insulator B are suitably sensitized or metallized by applying a saturated Water solution of lithinum molybdate thereto and thereafter firing the insulator body for three minutes at 2200 F. in a dry hydrogen atmosphere. This process is preferably repeated for two or three applications of the lithium molybdate solution to build up a very thin molybdenum coating on the surface of the ceramic body B. Thereafter, the molybdenum coated ceramic insulator body B is immersed in a suitable copper electroplating bath, which may be of any suitable composition; suitable electrodes are attach-ed to the sensitized surfaces; and a flash coating of copper is applied over the molybdenum. The copper plated bodies are thereafter washed and dried in preparation for the brazing operation now to be described. Alternatively, in some instance it may be desirable to flash coat with nickel in preparation for the copper plating. Where this is done the body is immersed in a mild electroplating bath of .any suitable composition; appropriate electrodes are then, attached to the sensitized surfaces; and a flash coating of nickel is applied over the molybdenum. Thereafter the nickel plated bodies may be washed, and copper plated, and then washed and dried, as above described, in preparation for the brazing operation.

The brazing operation is carried out by inserting a ring of a silver braze material upon the shoulder 24 of the casing A, and thereafter installing the insulator body B into its central opening to bring the shoulder 30 down upon the brazing material. Thebrazing material may be a ring of brazing wire or an annular ring of brazing shim stock. Thereafter the electrode rod 42 is inserted into the central opening 36 of the insulator body B until the collar 44 rests upon the end surface 46 of the enlarged bore portion 48, so as to exactly position the electrode with respect to the insulator body B. A similar ring of brazing materiaL'be it wire or shim stock, is thereafter placed upon the conical shoulder 40 in the region surrounding the electrode 42; and a Kovar eyelet 54 is thereafter teleseoped over the rod 42 and brought down into engagement with its ring of brazing material. The central opening 60 of the Kovar eyelet 54 has a diameter which is only one or two thousandths greater than the diameter of the upper end portion 50 of the rod 42, in order to provide a close adjusting fit with respect to the rod 50, for reasons which will later be explained. The exterior conical surface 58 of the eyelet 54 is likewise very accurately made, so that its surface closely matches that of the shoulder 40. A small ring of brazing material is thereafter telescoped over the rod 50 to rest against the upper surface of the eyelet 54 in the region adjacent the rod 50.

. The actual brazing operation is carried out by placing the above assembly of parts in an upright position in a brazing oven where the part is subject to a temperature of 1350 F. in a hydrogen atmosphere for four minutes. The rings of brazing material that are inserted between the various parts have an appreciable thickness prior to the melting of the brazing material. During the actual melting, this brazing material wets both the sensitized surfaces of the insulator body B, and the opposing metal surfaces and draws the parts together. It is a feature of the invention that the insulator body B is free to move downwardly to automatically center itself tightly up against the shoulder 24- of the casing A as the meltingoperation occurs, so that an absolute uniform and minimum thickness of brazing metal remains between the shoulders 24 and 30.

In similar manner, the eyelet 54 is free to move downwardly during the melting of its brazing materials; so that the eyelet 54 centers its outer conical surface 58 with respect to the conical surface 40, anadalso provides an absolutely uniform and minimum thickness of brazing material between the shoulder 40 of the insulator body B and the exterior surface 58 of the eyelet 54. At the same time the close fit of the eyelet 54 around the rod portion 50 holds the desired amount of brazing material between the upper surface of the eyelet 54 and the rod portion 50 so that,'uponcooling of the part, an absolute minimum thickness of metal remains between the various parts.

In some instances a copper brazing operation may be substituted for the silver brazing above described. The

procedure to be used is identical to that above described except that a temperature of approximately 2000 F. is used to completely melt the copper brazing material.

As a further feature of the invention, it will be seen that the metal bond between the electrode structure C and the insulator body B is confined to the region that is generally radially inwardly of the metal bond between the insulator body B and the casing A. The portion of the electrode C that is bonded to the insulator body B is made from a material whose coefficient of expansion closely matches that of the insulator body B. On the other hand, the casing structure A is made from a material which has a co-efficient of expansion that is approximately 50% greater than the co-efiicient of expansion of the insulator B. As a consequence, upon cooling from the brazing temperature, the joint between the insulator B and the casing A is placed under a slight compressive load.

The structure is sufliciently rigid in the region of the metallic bond to take this compressive load; and the amount'of compression that is produced is so controlled by the construction and composition of the metal seals that a slight compression remains, even in service..

As a further feature of the invention, the inner end of the insulator body B is held out of abutment with the casing structure A, and the lower end of the rod 42 is provided with a sliding fit with respect to the insulator body B, so that no axial force is placed upon the metallic bonds during use.

In some instances it may be desired to make the outer casing A of a material which has a sufliciently high coefficient of expansion to damage the metal bonds during cooling from the brazing temperatues. In the embodiment shown in FIG. 3, a conically shaped eyelet or washer 70 of a folded-over or U-shaped cross section is utilized to provide a pair of spaced apart leg portions 72 and 74 shaped to engage closely the shoulders 24 and 30 of the; casing A and insulator body B, respectively. The purpose of the eyelet 70 is to provide a flexible structure be-* tween the casing A and insulator member B which will.

accommodate the contraction of the casing A member quired in electrical discharge devices and the like. Inasmuch as this structure can accommodate the large expansions and contractions that occur in molten metal seals, it is to be expected that the structure can also be bonded together by molten ceramic material where the device 7 is to be used under condtions which are are not particularly severe.

While the invention has been described in considerable detail, it is not to be limited to the particular embodiments shown and described; as it is intended to cover hereby all novel adaptations, modifications, and arrangements thereof which come within the practice of those skilled in the art to which the invention relates.

What I claim is:

1. An electrical discharge device for use at temperatures below a predetermined elevated operating temperature and comprising: a tubular metal casing having an axially extending opening therethrough which is enlarged at its outer end to form an outwardly facing generally conically shaped shoulder, a tubular ceramic insulator body that is enlarged adjacent its outer end to provide a generally conically shaped shoulder which matches that of said casing, said casing having a positive thermal coeflicient of expansion that is slightly greater than the thermal c-oefiicient of expansion of said ceramic body, a gas impervious seal between said shoulders comprising a body of metal bonded to said conical shoulders by a layer of ductible brazing metal, said tubular insulator body having an axially extending electrode receiving opening therethrough, said electrode receiving opening being enlarged at its outer end to form an outwardly facing conical shoulder, a metallic electrode rod in said electrode receiving opening, said electrode having a portion positioned generally radially inwardly of said shoulders and which is made of a material having a coefiicient of expansion approximately equal to that of said insulator body, a conically shaped annular washer circumjacent said electrode rod, said washer having a conical surface for uniform abutment with said conical shoulder of said electrode receiving opening, and a brazed metal seal between said electrode and said washer and between said washer and said shoulder of said electrode receiving opening.

2. An electrical discharge device in accordance with claim 1, and wherein the inner end of said insulator body is unrestrained against axial expansion or contraction by said casing.

3. An electrical discharge device in accordance with claim 2, and wherein the inner end of said insulator body is axially guided with respect to said casing for accommodating relative axial movement in both directions and restraining relative radial movement.

4. An electrical discharge device in accordance with claim 3, and wherein said electrode portion is provided with a flange which is seated against the end surface of a radially enlarged portion of said electrode receiving opening beneath said annular washer.

5. An electrical discharge device in accordance with claim 4, and wherein said electrode portion and annular washer are made of a nickel-cobalt-iron alloy having a coefficient of thermal expansion between F. and 1000" F. of about 3.7 10- inches per inch per F., and said casing is made of a metal having a coefiicient of thermal expansion between 80 F. and 1000 F. of about 5.8 X 10- inches per inch per F.

'6. An electrical discharge device comprising, in combination, a tubular metal casing having an axially extending opening therethrough which is enlarged at its outer end to form an outwardly facing frusto-conically shaped shoulder, a tubular ceramic insulator body radially enlarged adjacent an outer end to provide a frusto-conically shaped shoulder which matches that of said casing, a brazed metal seal between said shoulders, said seal including a body of metal bonded to said conical shoulders by a layer of ductile brazen metal, said tubular insulator body having an axially extending electrode receiving opening therethrough, said electrode receiving opening being enlarged at its outer end to form an outwardly facing frusto-conical shoulder, a metallic electrode in said electrode receiving opening, a frusto-conically shaped annular washer circumjacent said electrode with the outer surface of said annular washer adjacent said conical shoulder of said electrode receiving opening, and a brazed metal seal between said electrode and said washer and between said washer and said shoulder of said electrode receiving opening.

7. In an electrical discharge device having a tubular metal casing cir-cumjacent a tubular ceramic insulator with an axially extending metallic electrode extending therethrough, the improvement comprising an enlarged portion at the outer end of the axial opening in said insulator forming a frusto-conical shoulder therein, a complementarily shaped, frusto-conical annular washer circumjacent said electrode and adjacent said frusto-conical shoulder in said insulator opening, and a brazed metal seal between said electrode and said Washer and between said washer and said shoulder.

References Cited by the Examiner UNITED STATES PATENTS 1,211,157 1/1917 Hughes 313 X 1,331,091 2/1920 Becker 313-144 X 2,311,647 2/1943 Doran 313l41 X 2,312,909 3/1943 Jeifery 313-144 X 2,317,305 4/ 1943 Schwartzwalder et al.

313--145 X 2,372,867 4/1945 Tognola 313138 2,937,296 5/1960 Logan 313-131 X 2,939,983 6/ 1960 Pierce et a1. 313-143 X GEORGE N. WESTBY, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,229,144 January 11, 1966 Milton E. Poland ied that error appears in the above numbered pat- It is hereby certif n and that the said Letters Patent should read as ent requiring correctio corrected below.

Column 6, line 23, before "in" insert rod Signed and sealed this 3rd day of January 1967.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer Commissioner of Patents EDWARD J. BRENNER 7 

1. AN ELECTRICAL DISCHARGE DEVICE FOR USE AT TEMPERATURES BELOW A PREDETERMINED ELEVATED OPERATING TEMPERATURE AND COMPRISING: A TUBULAR METAL CASING HAVING AN AXIALLY EXTENDING OPENING THERETHROUGH WHICH IS ENLARGED AT ITS OUTER END TO FORM AN INWARDLY FACING GENERALLY CONICALLY SHAPED SHOULDER, A TUBULAR CERAMIC INSULATOR BODY THAT IS ENLARGED ADJACENT ITS OUTER END TO PROVIDE A GENERALLY CONICALLY SHAPED SHOULDER WHICH MATCHES THAT OF SAID CASING, SAID CASING HAVING A POSITIVE THERMAL COEFFICIENT OF EXPANSION THAT IS SLIGHTLY GREATER THAN THE THERMAL COEFFICIENT OF EXPANSION OF SAID CERAMIC BODY, A GAS IMPERVIOUS SEAL BETWEEN SAID SHOULDERS COMPRISING A BODY OF METAL BONDED TO SAID CONICAL SHOULDERS BY A LAYER OF DUCTIBLE BRAZING METAL, SAID TUBULAR INSULATOR BODY HAVING AN AXIALLY EXTENDING ELECTRODE RECEIVING OPENING THERETHROUGH, SAID ELECTRODE RECEIVING OPENING BEING ENLARGED AT ITS OUTER END TO FORM AN OUTWARDLY FACING CONICAL SHOULDER, A METALLIC ELECTRODE ROD IN SAID ELECTRODE RECEIVING OPENING, SAID ELECTRODE HAVING A PORTION POSITIONED GENERALLY RADIALLY INWARDLY OF SAID SHOULDERS AND WHICH IS MADE OF A MATERIAL HAVING A COEFFICIENT OF EXPANSION APPROXIMATELY EQUAL TO THAT OF SAID INSULATOR BODY, A CONICALLY SHAPED ANNULAR WASHER CIRCUMJACENT SAID ELECTRODE ROD, SAID WASHER HAVING A CONICAL SURFACE FOR UNIFORM ABUTMENT WITH SAID CONICAL SHOULDER OF SAID ELECTRODE RECEIVING OPENING, AND A BRAZED METAL SEAL BETWEEN SAID ELECTRODE AND SAID WASHER AND BETWEEN SAID WASHER AND SAID SHOULDER OF SAID ELECTRODE RECEIVING OPENING. 